No-history method for intraocular lens power adjustment after excimer laser refractive surgery

Abstract

Systems and methods for using a new corneal ratio, referred to as the Geggel ratio, to estimate how much treatment a patient received at an original myopic or mixed astigmatism excimer laser refractive surgery. The Geggel ratio represents the ratio of the measure of a pre-IOL central pachymetry to a measure of a pre-IOL superior pachymetry. The estimated laser ablation depth (ELAD) is used in a derived linear regression equation to determine an IOL power adjustment that is added to the standard SRK/T formula used to determine IOL power.

1. A method for determining an intraocular lens (IOL) power for a patient having a refractively modified cornea, the method comprising:
 receiving an initial IOL power value determined using the SRK/T formula; 
 receiving a central pachymetry (CP) measurement and a superior corneal pachymetry (SCP) measurement for a cornea of the patient; 
 determining an estimated laser ablation depth by equating a first value to a second value, wherein the first value is a ratio of the sum of the CP measurement and the estimated laser ablation depth to the SCP measurement, and wherein the second value is related to a mean value of a sample of ratios of CP measurements to SCP measurements for a plurality of corneas that have not been refractively modified; 
 determining an IOL power adjustment value using the estimated laser ablation depth; and 
 adding the IOL power adjustment value to the initial IOL power to obtain a corrected IOL power value. 
 
     
     
       2. The method of  claim 1 , further comprising:
 performing a superior corneal pachymetry measurement and a central keratometry measurement on the cornea; and 
 calculating the initial IOL power using the superior corneal pachymetry and central keratometry measurements. 
 
     
     
       3. The method of  claim 1 , wherein the second value is one standard deviation above the mean value of the sample of ratios of CP measurements to SCP measurements for a plurality of corneas that have not been refractively modified. 
     
     
       4. The method of  claim 1 , wherein determining an IOL power adjustment value using the estimated laser ablation depth comprises:
 determining an estimated laser treatment amount by dividing the estimated laser ablation depth by a value related to known actual laser ablation depths per laser treatment amounts. 
 
     
     
       5. The method of  claim 4 , wherein the value related to known actual laser ablation depths per laser treatment amounts is equal to 12 micrometers per diopter (D). 
     
     
       6. The method of  claim 4 , wherein determining an IOL power adjustment value using the estimated laser ablation depth further comprises:
 inputting the estimated laser treatment amount into a derived regression equation. 
 
     
     
       7. The method of  claim 1 , wherein the second value is one standard deviation above the mean value of the sample of ratios of CP measurements to SCP measurements for a plurality of corneas that have not been refractively modified, and wherein determining an estimated laser ablation depth further comprises:
 comparing the estimated laser ablation depth to a minimum laser ablation depth; 
 if the estimated laser ablation depth is less than the minimum laser ablation depth, adding one standard deviation of the sample of ratios to the second value to obtain a third value; and 
 equating the first value to the third value. 
 
     
     
       8. The method of  claim 1 , wherein the second value is one standard deviation above the mean value of the sample of ratios of CP measurements to SCP measurements for a plurality of corneas that have not been refractively modified, and wherein determining an estimated laser ablation depth further comprises:
 comparing the estimated laser ablation depth to a maximum laser ablation depth; 
 if the estimated laser ablation depth is greater than the maximum laser ablation depth, subtracting one standard deviation of the sample of ratios from the second value to obtain a third value; and 
 equating the first value to the third value. 
 
     
     
       9. The method of  claim 1 , further comprising:
 determining a selectable IOL power value using the corrected IOL power value according to the following rules, wherein X represents an integer number of diopters:
 for corrected IOL power values of (X−1)+0.4 diopters to (X−1)+0.7 diopters, choose X diopters for the selectable IOL power value; and 
 for corrected IOL power values of (X−1)+0.8 diopters to (X)+0.3 diopters, choose (X+0.5) diopters for the selectable IOL power value. 
 
 
     
     
       10. A medical device configured to determine an intraocular lens (IOL) power for patients having a refractively modified cornea, the medical device comprising:
 a computing device; and 
 a tangible computer-readable medium having instructions stored thereon that, if executed by the computing device, cause the computing device to perform operations comprising:
 receiving an initial IOL power value determined using a formula; 
 receiving a central pachymetry (CP) measurement and a superior corneal pachymetry (SCP) measurement for a cornea of a patient; 
 determining an estimated laser ablation depth by equating a first value to a second value, wherein the first value is a ratio of the sum of the CP measurement and the estimated laser ablation depth to the SCP measurement, and wherein the second value is related to a mean value of a sample of ratios of CP measurements to SCP measurements for a plurality of corneas that have not been refractively modified; 
 determining an IOL power adjustment value using the estimated laser ablation depth; and 
 adding the IOL power adjustment value to the initial IOL power to obtain a corrected IOL power value. 
 
 
     
     
       11. The medical device of  claim 10 , wherein the formula is selected from the group consisting of the Hoffer formula, the SRK/T formula, the Holladay formula, and the Haigis formula. 
     
     
       12. The medical device of  claim 10 , further comprising:
 a measurement device operative to perform a superior corneal pachymetry measurement and a central keratometry measurement on a cornea of a patient. 
 
     
     
       13. The medical device of  claim 10 , wherein the operations further comprise:
 determining an estimated laser treatment amount by dividing the estimated laser ablation depth by a value related to known actual laser ablation depths per laser treatment amounts. 
 
     
     
       14. The medical device of  claim 10 , wherein the second value is one standard deviation above the mean value of the sample of ratios of CP measurements to SCP measurements for a plurality of corneas that have not been refractively modified, and wherein the operations further comprise:
 comparing the estimated laser ablation depth to a minimum laser ablation depth; 
 if the estimated laser ablation depth is less than the minimum laser ablation depth, adding one standard deviation of the sample of ratios to the second value to obtain a third value; and 
 equating the first value to the third value. 
 
     
     
       15. The medical device of  claim 10 , wherein the second value is one standard deviation above the mean value of the sample of ratios of CP measurements to SCP measurements for a plurality of corneas that have not been refractively modified, and wherein the operations further comprise:
 comparing the estimated laser ablation depth to a maximum laser ablation depth; 
 if the estimated laser ablation depth is greater than the maximum laser ablation depth, subtracting one standard deviation of the sample of ratios from the second value to obtain a third value; and 
 equating the first value to the third value. 
 
     
     
       16. A tangible computer-readable medium having instructions stored thereon that, if executed by a computing device, cause the computing device to perform operations comprising:
 receiving an initial IOL power value determined using a formula; 
 receiving a central pachymetry (CP) measurement and a superior corneal pachymetry (SCP) measurement for a cornea of a patient; 
 determining an estimated laser ablation depth by equating a first value to a second value, wherein the first value is a ratio of the sum of the CP measurement and the estimated laser ablation depth to the SCP measurement, and wherein the second value is related to a mean value of a sample of ratios of CP measurements to SCP measurements for a plurality of corneas that have not been refractively modified; 
 determining an IOL power adjustment value using the estimated laser ablation depth; and 
 adding the IOL power adjustment value to the initial IOL power to obtain a corrected IOL power value. 
 
     
     
       17. The tangible computer-readable medium of  claim 16 , wherein the formula is selected from the group consisting of the Hoffer formula, the SRK/T formula, the Holladay formula, and the Haigis formula. 
     
     
       18. The tangible computer-readable medium of  claim 16 , wherein the operations further comprise:
 determining an estimated laser treatment amount by dividing the estimated laser ablation depth by a value related to known actual laser ablation depths per laser treatment amounts. 
 
     
     
       19. The tangible computer-readable medium of  claim 16 , wherein the operations further comprise:
 calculating the initial IOL power using the SCP and CP measurements. 
 
     
     
       20. The tangible computer-readable medium of  claim 16 , wherein the second value is one standard deviation above the mean value of the sample of ratios of CP measurements to SCP measurements for a plurality of corneas that have not been refractively modified, and wherein the operations further comprise:
 comparing the estimated laser ablation depth to a minimum laser ablation depth; 
 if the estimated laser ablation depth is less than the minimum laser ablation depth, adding one standard deviation of the sample of ratios to the second value; 
 comparing the estimated laser ablation depth to a maximum laser ablation depth; and 
 if the estimated laser ablation depth is greater than the maximum laser ablation depth, subtracting one standard deviation of the sample of ratios from the second value.